1. Field of the Invention
The present invention relates to a laser working method and a laser working apparatus for cutting or welding workpieces, and more particularly, to a working method and apparatus in which a working head is moved for working.
2. Description of the Related Art
As a laser working machine and a laser working method in which a laser beam is applied to a workpiece to subject the workpiece to working, such as cutting, welding, etc., and a method and an apparatus characterized by a moving workpiece and fixed working head from which the laser beam is applied to the workpiece are known. For example, conventionally known are a method and an apparatus in which the workpiece to be worked is moved by utilizing a table which is movable in the directions perpendicularly intersecting X and Y axes.
Also known are a working method and an apparatus in which the working head is moved in the directions of the X, Y and Z axes for working, with the workpiece fixed.
The system, in which the working head is moved in the directions of the X, Y and Z axes with the workpiece fixed, requires a space for the movement of the workpiece, which is twice as long and wide as the workpiece or more. If the workpiece is a small one, this space will cause no special problem. If the size of the workpiece to be worked is as large as 5 m by 5 m, for example, a space of 10 m by 10 m is needed as a working space, so that the laser working machine is required to have larger dimensions.
If the system in which the working head is moved with the workpiece fixed is used, in order to solve the problem of the aforesaid space, however, the distance of laser beam propagation from a laser oscillator to a working point, that is, the optical path length, varies as the working head moves. If the optical path length varies, the diameter and quality of the laser beam change, so that working conditions, such as the optimum focal distance and focus depth, and the thickness of workable workpieces change. Thus, the working will become difficult, or will become unable to be effected under optimum conditions.
Thus, a system has been also developed in which the processing head can be moved without changing the optical path length, as shown in FIG. 6 (PRIOR ART) (see Published Examined Japanese Patent Application No. 1-55076). According to this system, a pair of reflectors 31, 31 for refracting a laser beam at 180.degree. are arranged in a laser beam propagation path, ranging from a laser oscillator 1 to a condensing lens 16 of a processing head 15, and the paired reflectors 31, 31 are moved for a distance, half as long as the movement stroke of the processing head 15, so that the optical path length will always remain constant.
As described above, if the processing head is fixed, a wide working space is required. If the processing head is designed for movement, on the other hand, the laser beam propagation characteristic changes, so that optimum working cannot be effected. According to the aforesaid system described in Published Examined Japanese Patent Application No. 1-55076, in which the processing head can be moved without changing the optical path length, the additional use of the two reflectors entails an increase in cost and power loss, and further such a system requires, in particular, a space for the movement of the paired reflectors for refracting tile laser beam at 180.degree.. If a workpiece to be worked is large-sized, this space must be so wide that a compact laser working machine cannot be obtained.